Pressure sensitive adhesive sheet for batteries and lithium-ion battery

ABSTRACT

A pressure sensitive adhesive sheet for batteries that includes a base material and a pressure sensitive adhesive layer provided on one surface side of the base material and containing inorganic fine particles. The haze value of the pressure sensitive adhesive layer is 50% or more and 85% or less.

TECHNICAL FIELD

The present invention relates to a pressure sensitive adhesive sheet forbatteries and a lithium-ion battery manufactured using the pressuresensitive adhesive sheet for batteries.

BACKGROUND ART

In some batteries, strip-like laminates are housed inside the batteriesin a state of being wound up. Such a laminate is formed by laminating apositive electrode, a negative electrode, and separators located betweenthe positive and negative electrodes. The positive and negativeelectrodes are connected to respective electrode lead-out tabs ofconductors, which electrically connect the positive and negativeelectrodes respectively to a positive electrode terminal and a negativeelectrode terminal of the battery.

A pressure sensitive adhesive sheet may be used as a stopper for theabove wound-up laminate and/or used for fixation of the electrodelead-out tabs to the electrodes. As such a pressure sensitive adhesivesheet, generally, a sheet composed of a base material and a pressuresensitive adhesive layer provided on one surface of the base material isused. From a viewpoint of improving the desired performance such asinsulation properties, a modified pressure sensitive adhesive sheet maybe used which is configured such that an insulation layer that containsan insulating material is provided on the surface of the above basematerial opposite to the above pressure sensitive adhesive layer orbetween the above base material and the above pressure sensitiveadhesive layer.

However, providing the insulation layer, as described above separatelyfrom the pressure sensitive adhesive layer may lead to an increase inthe manufacturing cost. In this regard, it is also tried to contain aninsulating material or the like in the pressure sensitive adhesive layerthereby to improve the insulation properties of the pressure sensitiveadhesive sheer, without providing an additional insulation layer, asdescribed above. For example, Patent Document 1 discloses a pressuresensitive adhesive sheet in which the pressure sensitive adhesive layercontains alumina. Patent Document 2 discloses a pressure sensitiveadhesive sheet in which the pressure sensitive adhesive layer containsmagnesium hydroxide, alumina, magnesium oxide, aluminum hydroxide,silica, boron nitride, titanium oxide, or magnesium carbonate.

PRIOR ART DOCUMENTS Patent Documents

[Patent Document 1] WO2017/038010

[Patent Document 2] JP2017-152372A

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

In recent years, as the energy density of batteries such as lithium ionbatteries is enhanced, if has become more important than ever to improvethe safety of batteries. For example, when foreign materials are mixedinside a battery, an internal short circuit may occur due to the foreignmaterials, and the battery may generate heat. When manufacturingbatteries, therefore, it is important to prevent such foreign materialsfrom being mixed and it is also important to properly find a battery inwhich foreign materials are mixed and remove the mixed foreign materialsor exclude the battery in which foreign materials are mixed.

When manufacturing batteries using the conventional pressure sensitiveadhesive sheet, however, if was very difficult to find the foreignmaterials interposed between the pressure sensitive adhesive sheet andan adherend.

The present invention has been made in consideration of such actualcircumstances and an object of the present invention is to provide apressure sensitive adhesive sheet for batteries that has high insulationproperties and allows the foreign materials mixed in a battery to bereadily found. Another object of the present invention is to provide alithium-ion battery m which the pressure sensitive adhesive sheet forbatteries is used.

Means for Solving the Problems

To achieve the above objects, first, the present invention provides apressure sensitive adhesive sheet for batteries, comprising: a basematerial; and a pressure sensitive adhesive layer provided on onesurface side of the base material and containing inorganic fineparticles, wherein the hate value of the pressure sensitive adhesivelayer is 50% or more and 65% or less (Invention 1).

In the pressure sensitive adhesive sheet for batteries according to theabove invention (Invention 1), the pressure sensitive adhesive layercontains inorganic fine particles and the haze value of the pressuresensitive adhesive layer falls within the above-described range, so thatthe pressure sensitive adhesive sheet for batteries can achieve highinsulation properties and allows the foreign materials interposedbetween the pressure sensitive adhesive sheet for batteries and anadherend to be readily found through the pressure sensitive adhesivesheet for batteries. Thus, the pressure sensitive adhesive sheet forbatteries can be used thereby to manufacture highly safe batteries inwhich foreign materials are suppressed from being mixed in thebatteries.

In the above invention (Invention 1), the total luminous transmittanceof the pressure sensitive adhesive layer may preferably be 80% or more(Invention 2).

In the above invention (Invention 1, 2), the content of the inorganicfine particles in the pressure sensitive adhesive layer may preferablybe 1 vol % or more and 50 vol % or less with respect to the pressuresensitive adhesive layer (Invention 3).

In the above invention (Invention 1 to 3), the thickness of the pressuresensitive adhesive layer may preferably be 1 μm or more and 50 μm orless (Invention 4).

Second, the present invention provides a lithium-ion battery in whichtwo or more conductors are fixed in a state of being m contact with eachother inside the battery using the above pressure sensitive adhesivesheet for batteries (Invention 1 to 4) (Invention 5).

Advantageous Effect of the Invention

The pressure sensitive adhesive sheet for batteries according to thepresent invention has high insular, ion properties and allows theforeign materials mixed in a battery to be readily found. Thelithium-ion battery manufactured using the pressure sensitive adhesivesheet for batteries can therefore have high safety.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of a pressure sensitive adhesive sheetfor batteries according to an embodiment of the present invention.

FIG. 2 is a partially cross-sectional, exploded perspective view of alithium-ion battery according to an embodiment of the present invention.

FIG. 3 is a developed, perspective view of an electrode body of thelithium-ion battery according to an embodiment of the present invention.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Hereinafter, one or more embodiments of the present invention will rcedescribed.

<Pressure Sensitive Adhesive Sheet for Batteries>

As illustrated in FIG. 1, a pressure sensitive adhesive sheet forbatteries 1 according to an embodiment of the present invention may becomposed of a base material. 11, a pressure sensitive adhesive layer 12provided on one surface side of the base material 11, and a releasesheet 13 provided on the surface side of the pressure sensitive adhesivelayer 12 opposite to the base material 11. In the pressure sensitiveadhesive sheet for batteries 1 according to the present embodiment, thepressure sensitive adhesive layer 12 contains inorganic fine particles121.

Here, the “pressure sensitive adhesive sheet for batteries” in thepresent description is a pressure sensitive adhesive sheet used at asite at which there is a possibility of contact with an electrolytesolution when manufacturing a battery. Preferably, it may be a pressuresensitive adhesive sheet used inside a battery and may also be apressure sensitive adhesive sheet for battery interior. The battery maypreferably be a nonaqueous battery. Accordingly, the electrolytesolution used in the battery may preferably be a nonaqueous electrolytesolution. The pressure sensitive adhesive sheet for batteries in thepresent description may preferably be a pressure sensitive adhesivesheet that is attached to a site at which there is a possibility ofimmersion in an electrolyte solution inside a nonaqueous battery or asite at which there is a possibility of contact with an electrolytesolution. A lithium-ion battery may be particularly preferred as thenonaqueous battery.

In the pressure sensitive adhesive sheet for batteries 1 according tothe present embodiment, the pressure sensitive adhesive layer 12contains the inorganic fine particles 121 and can thereby serve as aninsulation layer. The pressure sensitive adhesive sheet for batteries 1according to the present embodiment is therefore excellent in theinsulation properties in an ordinary state. Moreover, the pressuresensitive adhesive sheet for batteries 1 according to the presentembodiment includes the pressure sensitive adhesive layer 12, and theamount of neat generation can thereby be suppressed to a low value evenwhen the internal short circuit occurs m a battery in which the pressuresensitive adhesive sheet for batteries 1 is used.

In the pressure sensitive adhesive sheet for batteries 1 according tothe present embodiment, the haze value of the pressure sensitiveadhesive layer 12 is 50% or more and 85% or less, and the pressuresensitive adhesive layer 12 can thereby have appropriate translucency.This allows the presence of foreign materials to be readily foundthrough the pressure sensitive adhesive sheet for batteries 1 even whenthe foreign materials are interposed between the pressure sensitiveadhesive sheet for batteries 1 and an adherend. According to thepressure sensitive adhesive sheet for batteries 1 of the presentembodiment, therefore, a highly safe battery can be manufactured inwhich foreign materials are not mixed.

If the haze value of the pressure sensitive adhesive layer 12 exceeds85%, the pressure sensitive adhesive layer 12 will nor have sufficienttranslucency and it may be difficult to found the foreign materialspresent between the pressure sensitive adhesive sheet for batteries 1and an adherend. From this viewpoint, the haze value of the pressuresensitive adhesive layer 12 may foe preferably 82% or less andparticularly preferably 78% or less.

If the haze value of the pressure sensitive adhesive layer 12 is lessthan 50%, the pressure sensitive adhesive layer 12 will not contain asufficient amount of the inorganic fine particles 121, and the pressuresensitive adhesive sheet for batteries 1 cannot exhibit excellentinsulation properties. From this viewpoint, the haze value of thepressure sensitive adhesive layer 12 may be preferably 55% or more andparticularly preferably 80% or more. Details of the method of measuringthe above haze value are as described in the Testing Example, which willbe described later.

In the pressure sensitive adhesive sheet for batteries 1 according tothe present embodiment, the total luminous transmittance of the pressuresensitive adhesive layer 12 may be preferably 80% or more, particularlypreferably 88% or more, and further preferably 94% or more. When thetotal luminous transmittance of the pressure sensitive adhesive layer 12is 80% or more, the pressure sensitive adhesive layer 12 can have settertranslucency and allows the foreign materials present between thepressure sensitive adhesive sheet for batteries 1 and an adherend to befurther readily found through the pressure sensitive adhesive sheet forbatteries 1. On the other hand, the upper limit of the total luminoustransmittance of the pressure sensitive adhesive layer 12 is notparticularly limited, but may be, for example, 100% or less in anembodiment, 99% or less in another embodiment, and 97% or less in stillanother embodiment. Details of the method of measuring the above totalluminous transmittance are as described in the Testing Example, whichwill be described later.

1. Constitutional Elements 1-1. Base Material

In the pressure sensitive adhesive sheet for batteries 1 according tothe present embodiment, the base material 11 may preferably haveexcellent translucency. For example, the haze value of the base material11 may be preferably 30% or less, particularly preferably 20% or less,and further preferably 9% or less. On the other hand, the lower limit ofthe hate value of the base material 11 is not particularly limited, butmay be, for example, 0% or more in an embodiment, 0.1% or more inanother embodiment, and 1% or more in still another embodiment. Thetotal luminous transmittance of the base material 11 may be preferably20% or more, particularly preferably 35% or more, and further preferably50% or more. On the other hand, the upper limit of the total luminoustransmittance of the base material 11 is not particularly limited, butmay be, for example, 100% or less in an embodiment, 30% or less inanother embodiment, and 60% or less in still another embodiment. In thepressure sensitive adhesive sheet for batteries 1 according to thepresent embodiment, the pressure sensitive adhesive layer 12 hasexcellent translucency as previously described and, therefore, the basematerial 11 having excellent translucency allows the foreign materialspresent between the pressure sensitive adhesive sheet for batteries 1and an adherend to be further readily found through the pressuresensitive adhesive sheet for batteries 1. Details of the methods ofmeasuring the above-described haze value and total luminoustransmittance of the base material 11 are as described in the TestingExample, which will be described later.

The base material 11 may preferably have a high minimum voltage at whichinsulation breakdown occurs. For example, the minimum voltage may bepreferably 1 kV or higher, particularly preferably 2 kV or higher, andfurther preferably 5 kV or higher. When the minimum voltage is 2 kV orhigher, insulation breakdown of the base material 11 is less likely tooccur, and the reliability of the pressure sensitive adhesive sheet forbatteries 1 can be higher.

The base material 11 may preferably have flame retardancy that satisfiesthe flame retardancy level V-0 according to the UL 94 standard. When thebase material 11 has such flame retardancy, denaturation and deformationof the base material 11 can be suppressed even if the battery generatesheat due to its ordinary use. Moreover, even if troubles occur in thebattery and it generates excessive heat, ignition and/or burning of thebase material 11 can be suppressed to prevent a serious accident.

The material of the base material 11 can be appropriately selected fromthe viewpoints of insulation properties, flame retardancy, heatresistance, reactivity with an electrolyte solution, permeability to anelectrolyte solution, and the like. In particular, it may be preferredto use a resin film as the base material 11. Examples of the resin filminclude films of polyesters such as polyethylene terephthalate,polybutylene terephthalate and polyethylene naphthalate, polyolefinfilms such as a polyethylene film and a polypropylene film, films of apolymer that contains nitrogen in its main chain, such as a polyamidefilm, a polyimide film and a polyamideimide film, cellophane, a diacetylcellulose film, a triacetyl cellulose film, an acetyl cellulose butyratefilm, a polyvinyl chloride film, a polyvinylidene chloride film, apolyvinyl alcohol film, an ethylene-vinyl acetate copolymer film, apolystyrene film, a polycarbonate film, a polymethylpentene film, apolysulfone film, a polyether ether ketone film, a polyether sulfonefilm, a polyether imide film, a fluorine resin film, an acrylic resinfilm, a polyurethane resin film, a norbornene-based polymer film, acyclic clef in-based polymer film, a cyclic conjugated diene-basedpolymer film, a vinyl alicyclic hydrocarbon polymer film, other resinfilms, and laminated films thereof. In particular, from the viewpointsof insulation properties and flame retardancy, films of a polymer, thatcontains nitrogen in its main chain (the films may contain othercomponents than the polymer, here and hereinafter) may be preferred,films of a polymer that has a nitrogen-containing ring structure in themain chain may be particularly preferred, and films of a polymer thathas a nitrogen-containing ring structure and an aromatic ring structurein the main chain may be further preferred. Specifically, for example, apolyimide film, a polyetherimide film, or a polyether ether ketone film,may be preferred, among which the polyimide film may be preferredbecause it is particularly excellent in the insulation properties andflame retardancy.

The thickness of the base material 11 may be preferably 5 μm or more,particularly preferably 10 μm or more, and further preferably 15 μm ormore as the lower limit. When the lower limit of the thickness of thebase material 11 satisfies the above, breakage of the base material 11can be effectively suppressed even in a case in which, for example, anelectrode body configured such that an electrode lead-out tab is fixedby the pressure sensitive adhesive sheet for batteries 1 is wound up andthe winding pressure is applied to the pressure sensitive adhesive sheetfor batteries 1. From another aspect, the thickness of the base material11 may be preferably 200 μm or less, particularly preferably 100 μm orless, and further preferably 40 μm or less as the upper limit. When theupper limit of the thickness of the base material 11 satisfies theabove, the pressure sensitive adhesive sheet for batteries 1 can havemoderate flexibility and, even in a case in which the pressure sensitiveadhesive sheet for batteries 1 is attached to a surface having a heightdifference, such as in a case in which an electrode and an electrodelead-out tab are fixed to each other, the pressure sensitive adhesivesheet for batteries 1 can well follow the height difference.

1-2. Pressure Sensitive Adhesive Layer (1) Inorganic Fine Particles

The pressure sensitive adhesive layer 12 contains a pressure sensitiveadhesive component and also contains inorganic fine particles 121. Theinorganic fine particles 121 are not limited, provided that they canimpart desired insulation properties to the pressure sensitive adhesivelayer. 12 and can achieve the previously described haze value of thepressure sensitive adhesive layer 12. Examples for use include powdersof calcium carbonate, aluminum hydroxide, alumina, titania, silica,boehmite, talc, iron oxide, silicon carbide, barium sulfate, boronnitride, zirconium oxide, etc., beads obtained by pelletizing them,single crystal fibers, and glass fibers. These may each be used aloneand two or more types may also be used as a mixture. Among these, atleast one of calcium carbonate and aluminum hydroxide may be preferablyused from the viewpoints of achieving high insulation properties andreadily adjusting the haze value to the previously described range.

The average particle diameter of the inorganic fine particles 121 may bepreferably 0.01 μm or more, more preferably 0.1 μm or more, particularlypreferably 0.2 μm; or more, and further preferably 0.3 μm or more. Fromanother aspect, the average particle diameter of the inorganic fineparticles 121 may be preferably 10 μm or less, particularly preferably 5μm or less, and further preferably 1.4 μm or less. When the averageparticle diameter of the inorganic fine particles 121 falls within theabove range, the haze value of the pressure sensitive adhesive layer 12can be readily adjusted to the previously described range. When theaverage particle diameter of the inorganic fine particles 121 is 0.01 μmor more, the pressure sensitive adhesive sheet for batteries 1 accordingto the present embodiment can readily exhibit high insulationproperties. When the average particle diameter of the inorganic fineparticles 111 is 10 μm or less, the dispersibility of the inorganic fineparticles 121 is more excellent, and the occurrence of irregularities onthe surface of the pressure sensitive adhesive layer 12 opposite to thebase material 11 can be effectively prevented, so that excellentadhesive strength can be readily achieved. The average particle diameterof the inorganic fine particles 121 is to be measured by a laserdiffraction/scattering method.

The refractive index of the inorganic fine particles 121 may bepreferably 1.4 or more, particularly preferably 1.5 or more, and furtherpreferably 1.55 or more. From another aspect, the refractive index ofthe inorganic fine particles 121 may be preferably 2 or less,particularly preferably 1.3 or less, and more preferably 1.1 or less.When the refractive index of the inorganic fine particles 121 fallswithin the above range, the haze value of the pressure sensitiveadhesive layer 12 can be readily adjusted to the previously describedrange.

The above-described refractive index of the inorganic fine particle 121may be measured by the following method. That is, after a sample isprepared through placing the inorganic particles 121 on a slide glass,dropping a refractive index standard solution on the inorganic particles121, and covering them with a cover glass, the sample is observed with amicroscope, and the refractive index value of the refractive indexstandard solution when the profile of fine particles is most difficultto see is determined as the refractive index of the inorganic fineparticles 121.

The content of the inorganic fine particles 121 in the pressuresensitive adhesive layer 12 may be preferably 1 vol % or more,particularly preferably 5 vol % or more, and further preferably 10 vol %or more with respect to the pressure sensitive adhesive layer 12. Fromanother aspect the content of the inorganic fine particles 121 in thepressure sensitive adhesive layer 12 may be preferably 50 vol % or less,particularly preferably 40 vol % or less, and further preferably 30 vol% with respect to the pressure sensitive adhesive layer 12. When theinorganic fine particles 121 are contained in the pressure sensitiveadhesive layer 12 with the above-described range of the volume ratio,the haze value of the pressure sensitive adhesive layer 12 can bereadily adjusted to the previously described range. When theabove-described content is 1 vol % or more with respect to the pressuresensitive adhesive layer 12, the haze value of the pressure sensitiveadhesive layer 12 can be readily increased td a certain degree, and thepressure sensitive adhesive sheet for batteries 1 according to thepresent embodiment may readily exhibit high insulation properties. Whenthe above-described content is 50 vol % or less with respect to thepressure sensitive adhesive layer 12, the haze value of the pressuresensitive adhesive layer 12 can be readily reduced to a curtain degree,end the pressure sensitive adhesive sheet for batteries 1 according tothe present embodiment is more excellent in the suitability for foreignmaterial inspection.

The content of the inorganic fine particles 121 in the pressuresensitive adhesive layer 12 may be preferably 5 mass parts or more,particularly preferably 15 mass parts or more, and further preferably 25mass parts or more with respect to 100 mass parts of the pressuresensitive adhesive component contained in the pressure sensitiveadhesive layer 12. From another aspect, the content of the inorganicfine particles 121 in the pressure sensitive adhesive layer 12 may bepreferably 500 mass parts or less, particularly preferably 250 massparts or less, and further preferably 100 mass parts or less withrespect to 100 mass parts of the pressure sensitive adhesive componentcontained in the pressure sensitive adhesive layer 12. When theinorganic fine particles 121 are contained in the pressure sensitiveadhesive layer. 12 so that the content of the inorganic fine particles121 falls within the above-described range with respect to 100 massparts of the pressure sensitive adhesive component contained in thepressure sensitive adhesive layer 12, the volume ratio of the inorganicfine particles 121 contained in the pressure sensitive adhesive layer 12can be readily adjusted to the previously described range,

(2) Pressure Sensitive Adhesive Component

The pressure sensitive adhesive component contained in the pressuresensitive adhesive layer 12 is not particularly limited and can beappropriately selected from the viewpoints of solubility in anelectrolyte solution, flame retardancy, heat resistance, insulationproperties, and the like. In particular, it is preferred to use at leastone of an acrylic-based pressure sensitive adhesive component, asilicone-based pressure sensitive adhesive component, a rubber-basedpressure sensitive adhesive component, and a urethane-based pressuresensitive adhesive component as the pressure sensitive adhesivecomponent. The pressure sensitive adhesive component contained in thepressure sensitive adhesive layer 12 may be any of an emulsion type, asolvent type, or a non-solvent type and may also be any of a crosslinkedtype or a non-crosslinked type. Among the above, an acrylic-basedpressure sensitive adhesive component is preferred, a crosslinked-typeacrylic-based pressure sensitive adhesive component is 1.5 particularlypreferred, and a solvent and crosslinked-type acrylic-based pressuresensitive adhesive component is further preferred, from the viewpointsof ease of fine adjustment of the adhesive strength, etc.

The above-described acrylic-based pressure sensitive adhesive componentmay preferably be composed of a (meth)acrylic ester polymer (A) and acrosslinker (B). In this case, the pressure sensitive adhesive layer 12contains the acrylic-based pressure sensitive adhesive component, whichis composed of the (meth)acrylic ester polymer (A) and the crosslinker(B), and the inorganic fine particles 121. Such a pressure sensitiveadhesive layer 12 may preferably be formed of a pressure sensitiveadhesive composition that contains the (meth)acrylic ester polymer (A),the crosslinker (B), and the inorganic fine particles 121 (thiscomposition may be referred to as a “pressure sensitive adhesivecomposition P,” hereinafter).

As used in the present description, the term “(meth)acrylic ester”refers to both the acrylic ester and the methacrylic ester. The sameapplies to other similar terms. As used in the present description, theterm “polymer” encompasses the concept of a “copolymer.”

(2-1) (Meth)Acrylic Ester Polymer (A)

From the viewpoint that the pressure sensitive adhesive layer 12 canreadily have a high adhesion property to an adherend, the (meth)acrylicester polymer (A) may preferably contain (meth)acrylic alkyl ester ofwhich the carbon number of alkyl group is 1 to 10, as the monomer unitwhich constitutes the polymer. Examples of such (meth)acrylic alkylester include methyl (meth)acrylate, ethyl (meth)acrylate, propyl(meth)acrylate, n-hexyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl(meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate,and n-decyl (meth)acrylate. Among these, acrylic alkyl ester of whichthe carbon number of alkyl group is 3 to 9 is preferred, and acrylicalkyl ester of which the carbon number of alkyl group is 5 to 8 isparticularly preferred. These may each be used alone and two or moretypes may also be used in combination.

The (meth)acrylic ester polymer (A) may preferably contain 50 mass % ormore, particularly preferably 60 mass % or more, and further preferably70 mass % or more of the (meth)acrylic alkyl ester of which the carbonnumber of alkyl group is 1 to 10, as the monomer unit which constitutesthe polymer. When 50 mass % or more of the above (meth)acrylic alkylester is contained, the adhesion property to an adherend is moreimproved. From another aspect, the (meth)acrylic ester polymer (A) maypreferably contain 99 mass % or less, particularly preferably 95 mass %or less, and further preferably 90 mass % or less of the (meth)acrylicalkyl ester of which the carbon number of alkyl group is 1 to 10, as themonomer unit which constitutes the polymer. When the content of theabove (meth)acrylic alkyl ester is 99 mass % or less, an appropriateamount of other monomer components can be introduced into the(meth)acrylic ester polymer (A).

From the viewpoint that the pressure sensitive adhesive layer 12 canreadily have excellent electrolyte solution resistance, the(meth)acrylic ester polymer (A) may preferably contain (meth)acrylicalkyl ester of which the carbon number of alkyl group is 11 to 25, asthe monomer unit which constitutes the polymer. Examples of such(meth)acrylic alkyl ester include n-lauryl (meth)acrylate, myristyl(meth)acrylate, palmityl (meth)acrylate, and stearyl (meth)acrylate.Among these, (meth)acrylic alkyl ester of which the carbon number ofalkyl group is 12 to 18 is preferred. These may each be used alone andtwo or more types may also be used in combination.

The (meth)acrylic ester polymer (A) may preferably contain 1 mass % ormore, more preferably 5 mass % or more, and particularly preferably 10mass % or more of the (meth)acrylic alkyl ester of which the carbonnumber of alkyl group is 11 to 20, as the monomer unit which constitutesthe polymer. When the content is 1 mass % or more, the pressuresensitive adhesive layer 12 obtained can have a higher hydrophobicproperty, and more excellent electrolyte solution resistance can therebybe readily achieved. From another aspect, the (meth)acrylic esterpolymer. (A) may preferably contain 40 mass % or less, more preferably30 mass % or less, and particularly preferably 20 mass % or less of the(meth)acrylic alkyl ester of which the carbon number of alkyl group is11 to 20, as the monomer unit which constitutes the polymer. When 40mass % or less of the above (meth)acrylic alkyl ester, is contained, anappropriate amount of other monomer components can be readily introducedinto the (meth)acrylic ester polymer (A).

If desired, the (meth)acrylic ester polymer (A) may contain monomersother than the above as the monomer unit which constitutes the polymer.Examples of such monomers include a monomer that contains a reactivefunctional group and a monomer that does not contain a reactivefunctional group.

Examples of the monomer which contains a reactive functional group(reactive functional group-containing monomer) include a monomer havinga carboxy group in the molecule (carboxy group-containing monomer), amonomer having a hydroxyl group in the molecule (hydroxylgroup-containing monomer), and a monomer having an amino group in themolecule (amino group-containing monomer). The (meth)acrylic esterpolymer (A) may preferably contain the hydroxyl group-containing monomeror the carboxy group-containing monomer, among the above, as the monomerunit which constitutes the polymer, and may particularly preferablycontain the carboxy group-containing monomer as the monomer unit whichconstitutes the polymer. When the carboxy group-containing monomer, iscontained, the polarity of the pressure sensitive adhesive “layer” 12formed is high, and the resistance to dissolution into an electrolytesolution is more excellent.

Examples of the carboxy group-containing monomer include ethylenicallyunsaturated carboxylic acids ouch as acrylic acid, methacrylic acid,crotonic acid, maleic acid, itaconic acid, and citraconic acid. Amongthese, acrylic acid may be preferred. According to the acrylic acid, theabove effects may be more excellent. The above carboxy group-containingmonomers may each be used alone and two or more types may also be usedin combination.

Examples of the hydroxyl group-containing monomer include hydroxyalkyl(meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl(meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl(meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl(meth)acrylate. These may each be used alone and two or more types mayalso be used in combination.

Examples of the amino group-containing monomer include aminoethyl(meth)acrylate and n-butylaminoethyl (meth)acrylate. These may each beused alone and two or more types may also be used in combination.

The (meth)acrylic ester polymer (A) may preferably contain 0.5 mass % ormore, particularly preferably 1 mass % or more, and further preferably 3mass % or more of the reactive functional group-containing monomer asthe monomer unit which constitutes the polymer. From another aspect, the(meth)acrylic ester polymer (A) may preferably contain 30 mass % orless, particularly preferably 20 mass % or less, and further preferably9 mass % or less of the reactive functional group-containing monomer asthe monomer unit which constitutes the polymer. When the (meth)acrylicester, polymer (A) contains the above amount of the reactive functionalgroup-containing monomer as the monomer unit, a crosslinked structure iswell formed by the reaction with the crosslinker (B) to moderatelyenhance the cohesive strength of the pressure sensitive adhesive layer12 formed, and the resistance to dissolution into an electrolytesolution can thereby be more excellent.

Examples of the monomer which does not contain a reactive functionalgroup include alkoxyalkyl (meth)acrylates such as methoxyethyl(meth)acrylate and ethoxyethyl (meth)acrylate, (meth)acrylic estershaving a non-crosslinkable tertiary amino group, such asN,N-dimethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl(meth)acrylate and (meth)acryloyl morpholine, (meth)acrylamide, dimethylacrylamide, vinyl acetate, and styrene. These may each be used alone andtwo or more types may also be used in combination.

The (meth)acrylic ester polymer (A) may be a polymer obtained bysolution polymerization, a polymer, obtained by polymerization without asolvent, or a polymer obtained by emulsion polymerization. Among these,a solution polymerization product obtained by a solution polymerizationmethod may be preferred. Being a solution polymerization product allowsa high molecular-weight linear polymer to be easily obtained, and thepressure sensitive adhesive layer 12 can readily nave more excellentelectrolyte solution resistance.

The polymerization form of the (meth)acrylic ester polymer (A) may be arandom copolymer, and may also be a block copolymer.

The weight-average molecular weight of the (meth)acrylic ester polymer(A) may be preferably 50,000 or more, more preferably 100,000 or more,particularly preferably 200,000 or more, and further preferably 500,000or more as the lower limit. When the lower limit of the weight-averagemolecular weight of the (meth)acrylic ester polymer (A) satisfies theabove, the pressure sensitive adhesive layer 12 formed can have moreexcellent resistance to dissolution into an electrolyte solution.

From another aspect, the weight-average molecular weight of the(meth)acrylic ester polymer (A) may be preferably 2,500,000 or less,more preferably 2,000,000 or less, particularly preferably 1,200,000 orless, and further preferably 950,000 or less as the upper limit. Whenthe upper limit of the weight-average molecular weight of the(meth)acrylic ester polymer (A) satisfies the above, the adhesionproperty to an adherend can be more excellent. As used in the presentdescription, the weight-average molecular weight refers to a standardpolystyrene equivalent value that is measured using a gel permeationchromatography (GPC) method.

In the pressure sensitive adhesive composition P, one type of the(meth)acrylic ester polymer (A) may be used alene and two or more typesmay also be used in combination.

(2-2) Crosslinker (B)

It suffices that the crosslinker (B) is reactive with a reactivefunctional group of the (meth)acrylic ester polymer (A). Examples of thecrosslinker (B) include an isocyanate-based crosslinker, an epoxy-basedcrosslinker, an amine-based crosslinker, a melamine-based crosslinker,an aziridine-based crosslinker, a hydrazine-based crosslinker, analdehyde-based crosslinker, an oxazoline-based crosslinker, a metalalkoxide-based crosslinker, a metal chelate-based crosslinker, a metalsalt-based crosslinker, and an ammonium salt-based crosslinker. One typeof the crosslinker (B) may be used alone and two or more types may alsobe used in combination.

From the viewpoints of the reactivity with the reactive functional groupof the (meth)acrylic ester polymer (A), in particular, with the carboxygroup originated from the carboxy croup-containing monomer, theelectrolyte solution resistance after the reaction, the insulationproperties, etc., it may be preferred to use the isocyanate-basedcrosslinker among the above.

The isocyanate-based crosslinker contains at least a polyisocyanatecompound. Examples of the polyisocyanate compound include aromaticpolyisocyanates such as tolylene diisocyanate, diphenylmethanediisocyanate and xylylene diisocyanate, aliphatic polyisocyanates suchas hexamethylene diisocyanate, alicyclic polyisocyanates such asisophorone diisocyanate and hydrogenated diphenylmethane diisocyanate,biuret bodies and isocyanurate bodies thereof, and adduct bodies thatare reaction products with low molecular active hydrogen-containingcompounds such as ethylene glycol, propylene glycol, neopentyl glycol,trimethylol propane, and castor oil. Among these,trimethylolpropane-modified aromatic polyisocyanate may be preferred,and trimethylolpropane-modified tolylene diisocyanate andtrimethylolpropane-modified xylylene diisocyanate may be particularlypreferred, from the viewpoint of reactivity with hydroxyl groups.

The content of the crosslinker (B) in the pressure sensitive adhesivecomposition P tray be preferably 0.1 mass parts or more, particularlypreferably 0.5 mass parts or more, and further preferably 1 mass part ormore as the lower limit to 100 mass parts of she (meth)acrylic esterpolymer (A). From another aspect, the content may be preferably 20 massparts or less, particularly preferably 15 mass parts or less, andfurther preferably 10 mass parts or less as the upper limit. When thecontent of the crosslinker (B) fails within the above range, acrosslinked structure is well formed to moderately enhance the cohesivestrength of the pressure sensitive adhesive layer 12 formed, and theresistance to dissolution into an electrolyte solution can thereby bemore excellent.

(2-3) Additives

If desired, the pressure sensitive adhesive composition P can containone or more of various additives, such as a tackifier, an antioxidant, asoftening agent, and a filler, which are commonly used in anacrylic-based pressure sensitive adhesive. The additives whichconstitute the pressure sensitive adhesive composition P are deemed notto include a polymerization solvent and a dilutent solvent, which willbe described later.

(3) Production of Pressure Sensitive Adhesive Composition P

The pressure sensitive adhesive composition P can be produced throughproducing the (meth)acrylic ester polymer (A) and adding the inorganicfine particles 121 and, if desired, the crosslinker (B), additives, andthe like to the (meth)acrylic ester polymer (A) obtained.

The (meth)acrylic ester polymer (A) can be produced by polymerizing amixture of the monomers which constitute the polymer using acommonly-used radical, polymerization method. Polymerization of the(meth)acrylic ester polymer. (A) may preferably be carried out by asolution polymerization method, if desired, using a polymerizationinitiator. Note, however, that the present invention is not limited tothis, and the polymerization may be carried out without a solvent.Examples of the polymerization solvent include ethyl acetate, n-butylacetate, isobutyl acetate, toluene, acetone, hexane, and methyl ethylketone and two or more types thereof may also be used in combination.

Examples of the polymerization initiator include azo-based compounds andorganic peroxides and two or more types thereof may also be used incombination. Examples of the azo-based compounds include2,2′-azobisisobutyronitrile, 2,2′-azobis(2-methylbutyronitrile),1,1′-azobis(cyclohexane 1-carbonitrile),2,2′-azobis(2,4-dimethylvaleronitrile),2,2′-azobis(2,4-dimethyl-4-methoxyvaleronitrile), dimethyl2,2′-azobis(2-methylpropionate), 4,4′-azobis(4-cyanovaleric acid),2,2′-azobis(2-hydroxymethylpropionitrile), and2,2′-azobis[2-(2-imidazolin-2-yl)propane].

Examples of the organic peroxides include benzoyl peroxide, t-butylperbenzoate, cumene hydroperoxide, diisopropyl peroxydicarbonate,di-n-propyl peroxydicarbonate, di(2-ethoxyethyl)peroxydicarbonate,t-butyl peroxyneodecanoate, t-butyl peroxypivalate,(3,5,5-trimethylhexanoyl)peroxide, dipropionyl peroxide, and diacetylperoxide.

The weight-average molecular weight of the polymer to be obtained can beadjusted by compounding a chain transfer agent, such as2-mercaptoethanol, in the above polymerization step.

After the (meth)acrylic ester polymer (A) is obtained, the pressuresensitive adhesive composition P may be obtained through adding theinorganic fine particles 121 and, if desired, the crosslinker (B),additives, and the like to the solution of the (meth)acrylic esterpolymer (A) and sufficiently mixing them.

For adjustment of a suitable viscosity for coating and/or adjustment ofa desired film thickness of the pressure sensitive adhesive layer 12,the pressure-sensitive adhesive composition P may be appropriatelydiluted with a diluent solvent or the like in addition to the previouslydescribed polymerization solvent to obtain a coating liquid, which willbe described later. Examples of the diluent solvent include ethylacetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane,and methyl ethyl ketone and two or more types thereof may also be usedin combination.

(4) Crosslinking of Pressure Sensitive Adhesive Composition P

When the pressure sensitive adhesive composition P contains thecrosslinker (B), the pressure sensitive adhesive layer 12 can be formedby crosslinking the pressure sensitive adhesive composition P.Crosslinking of the pressure sensitive adhesive composition P can beusually carried out by heating treatment. The heating treatment can alsoserve as drying treatment when volatilizing the diluent solvent and thelike from the coating film of the pressure sensitive adhesivecomposition P applied to a desired object.

The heating temperature of the heating treatment may be preferably 50°C. to 1.50° C. and particularly preferably 70° C. to 120° C. The heatingtime may be preferably 30 seconds to 10 minutes and particularlypreferably 50 seconds to 5 minutes.

After the heating treatment, if necessary, an aging period at anordinary temperature (e.g., 23° C., 50% RH) for about 1 to 2 weeks maybe provided. When the aging period is necessary, the pressure sensitiveadhesive layer 12 is formed after the aging period passes, while whenthe aging period is nor necessary, the pressure sensitive adhesive layer12 is formed after the heating treatment is completed.

(5) Thickness of Pressure Sensitive Adhesive Layer

The thickness (a value measured in accordance with JIS K7130) of thepressure sensitive adhesive layer 12 may be preferably 1 μm or more,particularly preferably 3 μm or more, and further preferably 5 μm ormore as the lower limit. When the lower limit of the thickness of thepressure sensitive adhesive layer 12 satisfies the above, the pressuresensitive adhesive sheet for batteries 1 can readily exhibit highinsulation properties. From another aspect, the thickness of thepressure sensitive adhesive layer 12 may be preferably 50 μm or less,particularly preferably 20 μm or less, and further preferably 20 μm orless as the upper limit. When the upper limit of the thickness of thepressure sensitive adhesive layer 12 satisfies the above, the hate valueof the pressure sensitive adhesive layer 12 can be readily adjusted tothe previously described range. Moreover, when the upper limit of thethickness or the pressure sensitive adhesive layer 12 satisfies theabove, the amount of electrolyte solution infiltrating into the pressuresensitive adhesive layer 12 from its end parts can be effectivelyreduced.

The thickness of the pressure sensitive adhesive layer 12 may bepreferably 1.1 times or more, more preferably 5 times or more,particularly preferably 10 times or more, and further preferably 15times or more of the average particle diameter of the inorganic fineparticles 121. When the thickness of the pressure sensitive adhesivelayer 12 is 1.1 times or more of the average particle diameter of theinorganic fine particles 121, the surface smoothness of the pressuresensitive adhesive layer 12 is more excellent, and high adhesivestrength can be effectively obtained. The upper limit of the thicknessratio of the pressure sensitive adhesive layer 12 based on the averageparticle diameter of the inorganic fine particles 121 is notparticularly limited, but may be preferably 100 times or less, morepreferably 60 times or less, and particularly preferably 20 times orless.

1-3. Release Sheet

The release sheet 13 is to protect the pressure sensitive adhesive layer12 until the use of the pressure sensitive adhesive sheet for batteries1 and is removed when using the pressure sensitive adhesive sheet forbatteries 1. In the pressure sensitive adhesive sheet for batteries 1according to the present embodiment, the release sheet 13 may notnecessarily be required.

Examples of the release sheet 13 for use include a polyethylene film, apolypropylene film, a polybutene film, a polybutadiene film, apolymethylpentene film, a polyvinyl chloride film, a vinyl chloridecopolymer film, a polyethylene terephthalate film, a polyethylenenaphthalate film, a polybutylene terephthalate film, a polyurethanefilm, an ethylene-vinyl acetate film, an ionomer resin film, anethylene-(meth)acrylic acid copolymer film, an ethylene-(meth)acrylicester copolymer film, a polystyrene film, a polycarbonate film, apolyimide film, a fluorine resin film, and a liquid crystal polymerfilm. Crosslinked films thereof may also be used. A laminate filmobtained by laminating a plurality of such films may also be used.

It may be preferred to perform release treatment for the release surface(surface to be in contact with the pressure sensitive adhesive layer 12)of the release sheet 13. Examples of a release agent to be used for therelease treatment include alkyd-based, silicone-based, fluorine-based,unsaturated polyester-based, polyolefin-based, and wax-based releaseagents.

The thickness of the release sheet 13 is not particularly limited, butmay be usually about 20 to 150 μm.

2. Physical Properties, Etc. of Pressure Sensitive Adhesive Sheet forBatteries (1) Haze Value of Pressure Sensitive Adhesive Sheet forBatteries

The haze value of the pressure sensitive adhesive sheet for batteries 1(excluding the release sheet 13) according to the present embodiment maybe preferably 90% or less, particularly preferably 85% or less, andfurther preferably 80% or leas. When the haze value of the pressuresensitive adhesive sheet for batteries 1 is 90% or less, the foreignmaterials present between the pressure sensitive adhesive sheet forbatteries 1 and an adherend can be more readily found. In the pressuresensitive adhesive sheet for batteries 1 according to the presentembodiment, the haze value of the pressure sensitive adhesive layer 12alone falls within the previously described range, and the haze value ofthe pressure sensitive adhesive sheet for batteries 1 (excluding therelease sheet 13) can thereby be readily adjusted to a relatively lowvalue as the above. The lower limit of the hate value of the pressuresensitive adhesive sheet for batteries 1 (excluding the release sheet13) is not particularly limited, and may be, for example, 50% or more inan embodiment, 56% or more in another embodiment, and 62% or more instill another embodiment. Details of the method of measuring the hatevalue of the pressure sensitive adhesive sheet for batteries 1(excluding the release sheet 13) are as described in the TestingExample, which will be described later.

(2) Total Luminous Transmittance of Pressure Sensitive Adhesive Sheetfor Batteries

The total luminous transmittance of the pressure sensitive adhesivesheet for batteries 1 (excluding the release sheet 13) according to thepresent embodiment may be preferably 20% or more, particularlypreferably 35% or more, and further preferably 50% or more. When thetotal luminous transmittance of the pressure sensitive adhesive sheetfor batteries 1 is 20% or more, the foreign materials present betweenthe pressure sensitive adhesive sheet for batteries 1 and an adherendcan be further readily found. In the pressure sensitive adhesive sheetfor batteries 1 according to the present embodiment, the haze value ofthe pressure sensitive adhesive layer 12 alone falls within thepreviously described range, and the total luminous transmittance of thepressure sensitive adhesive sheet for batteries 1 (excluding the releasesheet 13) can thereby be readily adjusted to a relatively high value asthe above. The upper limit of the total luminous transmittance of thepressure sensitive adhesive sheet for batteries 1 (excluding the releasesheet 13) is not particularly limited, and may be, for example, 100% orless in an embodiment, 80% or less in another embodiment, and 60% orless in still another embodiment. Details of the method of measuring thetotal luminous transmittance of the pressure sensitive adhesive sheetfor batteries 1 (excluding the release sheet 13) are as described in theTesting Example, which will be described later.

(3) Adhesive Strength

The adhesive strength of the pressure sensitive adhesive sheet forbatteries 1 according to the present embodiment to an aluminum plate maybe preferably 0.5 N/25 mum or more and more preferably 1.0 N/25 mm ormore as the lower limit. When the lower limit of the adhesive strengthof the pressure sensitive adhesive sheet for batteries 1 satisfies theabove, a trouble is less likely to occur that the pressure sensitiveadhesive sheet for batteries 1 delaminates from an adherend (inparticular, from a metal member). The upper limit of the above adhesivestrength is not particularly limited, but may be preferably 50 N/25 mmor less in general, more preferably 40 N/25 mm or less, particularlypreferably 30 N/25 mm or less, and further preferably 5 N/25 nm or less.As used in the present description, the adhesive strength refersbasically to a peel strength that is measured using a method of 180°peeling in accordance with JIS Z0237: 2009. Details of the method ofmeasurement are as described in the Testing Example, which will bedescribed later.

(4) Insulation Properties (Rise in Temperature Due to Forced InternalShort Circuit Test)

When the forced internal short circuit test for a battery is performedin accordance with JIS C8714: 2007 using the pressure sensitive adhesivesheet for batteries 1 (excluding the release sheet 13) and small nickelpieces of a standard size (height 0.2 mm, width 0.1 mm, L-shaped with aside of 1 mm, angle 90°), the rise in temperature of the battery sidesurface may be preferably 30° C. or less, particularly preferably 20° C.or less, and further preferably 15° C. or less. When using small nickelpieces of a larger size (height 0.5 mm, width 0.2 mm, L-shaped with aside of 3 mm, angle 90°) than the standard size, the rise in temperatureof the battery side surface may be preferably 100° C. or less,particularly preferably 50° C. or less, and further preferably 30° C. orless. Details of the forced internal short, circuit test are asdescribed in the Testing Example, which will be described later.

It can be said that when the rise in temperature due to the forcedinternal short circuit test satisfies the above, the pressure sensitiveadhesive sheet for batteries 1 has high insulation properties, and abattery manufactured using the pressure sensitive adhesive sheet forbatteries 1 can have high safety. The pressure sensitive adhesive sheetfor batteries 1 according to the present embodiment includes thepressure sensitive adhesive layer 12, which contains the inorganic fineparticles 121, thereby to allow the rise in temperature due to theforced internal short circuit tear, to be suppressed low as the above.

(5) Thickness of Pressure Sensitive Adhesive Sheet for Batteries

The thickness of the pressure sensitive adhesive sheet for batteries 1(excluding the thickness of the release sheet 13) may be preferably 10μm or more, particularly preferably 10 μm or more, and furtherpreferably 20 μm or more. From, another aspect, the thickness of thepressure sensitive adhesive sheet, for batteries 1 may be preferably 250μm or less, particularly preferably 110 μm or less, and furtherpreferably 45 nm or less. When the thickness of the pressure sensitiveadhesive sheet for batteries 1 is 10 μm or more, both the excellentadhesion strength and the high insulation properties can be readilyachieved. When the thickness of the pressure sensitive adhesive sheetfor batteries 1 is 250 μm or less, the pressure sensitive adhesive sheetfor batteries 1 can have better translucency and allows the foreignmaterials present between the pressure sensitive adhesive sheet forbatteries 1 and an adherend to be readily found through the pressuresensitive adhesive sheet for batteries 1.

3. Method of Manufacturing Pressure Sensitive Adhesive Sheet forBatteries

The method of manufacturing the pressure sensitive adhesive sheet forbatteries 1 according to the present embodiment is not particularlylimited, provided that the pressure sensitive adhesive layer 12 can beformed on one side of the base material 11. For example, the releasesurface or the release sheet 13 may be coated with a coating liquid thatcontains the previously described pressure sensitive adhesivecomposition P and may further contain a solvent, if desired, and heatingtreatment may be performed to form a coating film. The coating filmformed as such may be the pressure sensitive adhesive layer 12 if anaging period is not necessary. If the aging period is necessary, theformed coating film may become the pressure sensitive adhesive layer 32after the aging period passes. Conditions for the heating treatment andaging are as previously described. Subsequently, after one surface ofthe base material 11 is attached to the surface of the formed pressuresensitive adhesive layer 12 opposite to the release sheet 13 and, ifnecessary, an aging period may be provided, the pressure sensitiveadhesive sheet for batteries 1 can be obtained.

Drying treatment when volatilizing a diluent solvent and the like of thecoating liquid can also serve as the above heating treatment. Whenperforming the heating treatment, the heating temperature may bepreferably 50° C. to 150° C. and particularly preferably 70° C. to 120°C. The heating time may be preferably 30 seconds to 10 minutes andparticularly preferably 50 seconds to 2 minutes. After the heatingtreatment, if necessary, an aging period at an ordinary temperature(e.g., 23° C., 50% RH) for about 1 to 2 weeks may be provided.

Another method of manufacturing the pressure sensitive adhesive sheetfor batteries 1 according to the present embodiment may include coatingthe base material 13 with the pressure sensitive adhesive composition Pand then forming the pressure sensitive adhesive layer 32 on the basematerial 11 thereby to obtain the pressure sensitive adhesive sheet forbatteries 1. Coating with the pressure sensitive adhesive composition P,heating treatment, and aging in this case can be performed as in thepreviously described method.

<Lithium-Ion Battery>

The lithium-ion battery according to an embodiment of the presentinvention may be configured such that two or more conductors are fixedin a state of being in contact with each other inside the battery usingthe previously described pressure sensitive adhesive sheet for batteries1. It may be preferred that at least one of the two or more conductorsbe in a sheet-like shape while at least another one be in a line-like ortape-like shape. The lithium-ion battery according to a preferredembodiment will be described below.

As illustrated in FIG. 2, the lithium-ion battery 2 according to thepresent embodiment may include a bottomed cylindrical exterior body 21of which the bottom part constitutes a negative electrode terminal 23, apositive electrode terminal 22 provided at an opening part of theexterior body 21, and an electrode body 24 provided inside the exteriorbody 21. An electrolyte solution may be enclosed in the lithium-ionbattery 2.

The electrode body 24 may include a positive electrode collector 241laminated with a positive electrode active material layer 241 a, anegative electrode collector 242 laminated with a negative electrodeactive material layer 242 a, and separators 243 interposed therebetween.The laminate of the positive electrode collector 241 and the positiveelectrode active material layer 241 a may be referred to as a positiveelectrode while the laminate of the negative electrode collector 242 andthe negative electrode active material layer 242 a may be referred to asa negative electrode, and the positive electrode and the negativeelectrode may be collectively referred to as an electrode or electrodes.The positive electrode, the negative electrode, and the separators 243may be wound up together and then inserted inside the exterior body 21.

As illustrated in FIG. 3, a line-like or tape-like electrode lead-outtab 244 may be attached to the positive electrode collector 241 usingthe previously described pressure sensitive adhesive sheet for batteries1, and the electrode lead-out tab 244 can thereby be electricallyconnected to the positive electrode collector 241. The electrodelead-out tab 244 may be electrically connected also to the abovepositive electrode terminal 22. The negative electrode collector 242 maybe electrically connected to the negative electrode terminal 23 via anelectrode lead-out tab which is not illustrated.

In general, the positive electrode collector 241 and the negativeelectrode collector 242 may be made of a material of metal such asaluminum while the electrode lead-out tab 244 may be made of a materialof metal such as aluminum or cooper.

The electrolyte solution used m the lithium-ion battery 2 may ordinarilybe a nonaqueous electrolyte solution. Preferred examples of thenonaqueous electrolyte solution include those in which a lithium salt asthe electrolyte is dissolved in a mixed solvent of a cyclic carbonateester and a lower chain carbonate ester.

Examples of the lithium salt for use include fluorine-based complexsalts, such as lithium hexafluorophosphate (LiPF₆) and lithiumborofluoride (LiBF₄), and LiN(SO₂Rf)₂.LiC(SO₂Rf)₃ (where Rf=CF₃, C₂F₅).Examples of the cyclic carbonate ester for use include ethylenecarbonate and propylene carbonate. Preferred examples of the lower chaincarbonate ester include dimethyl carbonate, ethyl methyl carbonate, anddiethyl carbonate.

The lithium-ion battery 2 according to the present embodiment can bemanufactured by an ordinary method except that the previously describedpressure sensitive adhesive sheet for batteries 1 is used for fixationof the electrode lead-out tab 244.

in the lithium-ion battery 2 according to the present embodiment, theelectrode lead-out tab 244 is attached to the positive electrodecollector 241 using the pressure sensitive adhesive sheet for batteries1. In the pressure sensitive adhesive sheet for batteries 1, even ifforeign materials are mixed between the pressure sensitive adhesivesheet for batteries 1 and an adherend, the foreign materials can bereadily found because the haze value of the pressure sensitive adhesivelayer 12 is 50% or more and 85% or less. It is therefore possible toprevent the occurrence of internal short circuit due to the presence offoreign materials. Moreover, the pressure sensitive adhesive sheet forbatteries 1 includes the pressure sensitive adhesive layer 12, whichcontains the inorganic fine particles 121, thereby to have highinsulation properties, and even if internal short circuit occurs, thetemperature rise due to the internal short circuit can be suppressedlow. Thus, the lithium-ion battery 2 according to the present embodimenthas high safety.

It should be appreciated that the embodiments heretofore explained aredescribed to facilitate understanding of the present invention and arenot described to limit the present invention. It is therefore intendedthat the elements disclosed in the above embodiments include all designchanges and equivalents to fall within the technical scope of thepresent invention.

For example, in the pressure sensitive adhesive sheet for batteries 1,the release sheet 13 may be omitted. In an embodiment, the pressuresensitive adhesive sheet for batteries 1 may be provided with one ormore other layers between the base material 11 and the pressuresensitive adhesive layer 12.

EXAMPLES

Hereinafter, the present invention will be described furtherspecifically with reference to examples, etc., but the scope of thepresent invention is not limited to these examples, etc.

Example 1 1. Preparation of Coating Liquid of Pressure SensitiveAdhesive Composition

A (meth)acrylic ester polymer was prepared using a solutionpolymerization method to copolymerize 80 mass parts of 2-ethylhexylacrylate, 11 mass parts of lauryl methacrylate, and 5 mass parts ofacrylic acid. The molecular weight of this polymer was measured usinggel permeation chromatography (GPC), which will be described later. Theweight-average molecular weight (Mw) was 750,000.

Then, 100 mass parts (solid content equivalent, here and hereinafter) ofthe obtained (meth)acrylic ester polymer and 3.72 mass parts oftrimethylolpropane-modified tolylene diisocyanate (available fromTOYOCHEM CO., LTD., trade name “BHS3515”) as an isocyanate-basedcrosslinker were mixed and diluted with ethyl acetate to obtain adiluted liquid having a solid concentration of 30%. The diluted liquidcontains, as the pressure sensitive adhesive component, the above(meth)acrylic ester polymer and the above isocyanate-based crosslinker.

For the diluted liquid thus obtained, 27.5 mass parts of calciumcarbonate fine particles (available from Konoshima Chemical Co., Ltd.,product name “Calcium Carbonate Light,” average particle diameter: 1.1μm, refractive index: 1.69) were added to 100 mass parts of the abovepressure sensitive adhesive component, and they were mixed to obtain acoating liquid of the pressure sensitive adhesive composition.

2. Formation of Pressure Sensitive Adhesive Layer

A release sheet (available from LINTEC Corporation, trade name“SP-PET251130”) was prepared in which one surface of a polyethyleneterephthalate film was subjected to release treatment using asilicone-based release agent. The release-treated surface of the releasesheet was coated with the coating liquid of the pressure sensitiveadhesive composition obtained in the above step 1 using a knife coaterand the obtained coating film was dried at 120° C. for 1 minute to forma pressure sensitive adhesive layer, having a thickness of 9 μm. Alaminate composed of the release-sheet end the pressure sensitiveadhesive layer, was thus obtained. The content of the inorganic fineparticles in the pressure sensitive adhesive layer formed was measuredby a method to be described later. The content was 10 vol %.

3. Production of Pressure Sensitive Adhesive Sheet for Batteries

The surface of the laminate, obtained in the above step 2, on the sideof the pressure sensitive adhesive layer and one surface of a polyimidefilm (available from DU PONT-TORAY CO., LTD., product name “Kapton100H,” thickness: 25 μm, flame retardation level according to UL94standard: V-0, haze value as measured by Testing Example 1 to bedescribed later: 6.01%, total luminous transmittance as measured byTesting Example 1 to be described later: 53.6%) as a base material wereattached to each other and they were then aged at 23° C. and 50% RH for7 days to obtain a pressure sensitive adhesive sheet for batteries inwhich the base material, the pressure sensitive adhesive layer, and therelease sheet were laminated in this order.

Here, the previously described weight-average molecular weight (Mw)refers to a weight-average molecular weight that is measured as astandard polystyrene equivalent value under the following conditionusing gel permeation chromatography (GPC) (GPC measurement).

<Measurement Condition>

GPC measurement apparatus: HLC-8320 available from Tosoh Corporation

GPC columns (passing through in the following order): available fromTosoh Corporation

TSK gel super H-H

TSK gel super HM-H

TSK gel super H2000

Solvent for measurement: tetrahydrofuran

Measurement temperature: 40° C.

The previously described content (vol %) of the inorganic fine particlesin the pressure sensitive adhesive layer was measured as follows. First,the pressure sensitive adhesive layer formed was burnt and the content(mass %) of the inorganic fine particles was measured from the obtainedasn, in accordance with JIS K 7250-1: 2006. On the other hand, the truedensity of the used inorganic fine particles was measured in accordancewith JIS Z8807: 2012. Furthermore, the density of the pressure sensitiveadhesive layer, formed was measured in accordance with JIS Z8807: 2012.The content (vol %) of the inorganic fine particles in the pressuresensitive adhesive layer was calculated on the basis of the measuredvalues thus obtained as the above of the content (mass %) of theinorganic fine particles, the true density of the inorganic fineparticles, and the density of the pressure sensitive adhesive layer.

Examples 2 to 3 and Comparative Examples 1 to 5

Pressure sensitive adhesive sheets for batteries were manufactured inthe same manner as in Example 1 except that the type and additive amountof the inorganic fine particles were changed as listed in Table 1. Theindication “-” in Comparative Example 3 means that inorganic fineparticles were not used.

<Testing Example 1> (Measurement of Mate Value and Total LuminousTransmittance)

For the pressure sensitive adhesive sheets for batteries (excluding therelease sheets) obtained in Examples and Comparative Examples, thepressure sensitive adhesive layers formed in Examples and ComparativeExamples, and the base materials used in Examples and ComparativeExamples, the haze value (%) and the total luminous transmittance (%)were measured using a haze meter (available from NIPPON DENSHOKUINDUSTRIES CO., LTD., product name “NDH-5000”). Results for the pressuresensitive adhesive sheets for batteries and the pressure sensitiveadhesive layers are listed in Table 1.

<Testing Example 2> (Measurement of Adhesive Strength)

The adhesive strength of the pressure sensitive adhesive sheets forbatteries in this Testing Example was measured in accordance with JISZ0237: 2009 except the following operation.

The pressure sensitive adhesive sheet for batteries obtained in each ofExamples and Comparative Examples was cut into a width of 2.5 mm and alength of 250 mm and the release sheet was then removed to obtain a testpiece. The exposed pressure sensitive adhesive layer of the test piecewas attached to an aluminum plate as an adherend using a rubber rollerof 2 kg under an environment of 23° C. and 50% RH. Immediatelythereafter, the test piece was peeled off from the above aluminum plateat a peel angle of 180° and a peel speed of 100 mm/min using a universaltensile tester (available from ORIENTEC Co., LTD., product name“TENSILON UTM-4-100”) and the adhesive strength (N/25 mm) was thuspleasured. Results are listed in Table 1.

<Testing Example 3> (Evaluation of Suitability for Foreign MaterialInspection)

The pressure sensitive adhesive sheet for batteries obtained in each ofExamples and Comparative Examples was cut into a size of 20 cm×20 mm toobtain a test piece. Subsequently, the release sheet was released fromone end of the test piece to partially expose the surface of thepressure sensitive adhesive layer opposite to the base material. Then,about 50 particles of white metal powder having a size of about 20 μmsquare as foreign materials were placed on the exposed surface of thepressure sensitive adhesive layer, and the released release sheet wasthereafter attached again to the pressure sensitive adhesive layer.Then, the above-described foreign materials were visually observed fromthe surface of the pressure sensitive adhesive sheet for batteries onthe side of the base material, and the suitability for foreign materialinspection was evaluated in accordance with the following criteria.Results are listed in Table 1.

o: Foreign materials were able to be confirmed well, and the suitability for inspection was sufficient when used in a battery.

x: Foreign materials were not able to be confirmed, and the suitabilityfor inspection was insufficient when used in a battery.

<Testing Example 4> (Evaluation of Battery Insulation Properties) (1)Production of Positive Electrode

A positive electrode paste was prepared by mixing 100 mass parts ofLiNi_(0.82)Co_(0.15)Al_(0.03)O₂ as a positive electrode active material,1.0 mass parts of acetylene black, 0.9 mass parts of polyvinylidenefluoride (binder), and an appropriate amount of NMP. Both surfaces ofaluminum foil to be a positive electrode collector having a thickness of20 μm were coated with the obtained positive electrode paste, which wasdried and then rolled to produce a strip-like positive electrode havinga width of 58 mm. Both surfaces near the center in the longitudinaldirection of the positive electrode were provided with slit-like exposedparts exposed from one end part to the other end part of the positiveelectrode collector in its width direction. The width W of the exposedparts was set to 6.5 mm.

Then, a strip-like aluminum positive electrode lead having a width of3.5 mm and a length of 68 mm was overlapped and aligned with an exposedpart of the positive electrode collector so that the length of thelead-out part would be 15 mm and the length of the overlapping partwould be 53 mm, and the overlapping part was welded to the exposed part.

Thereafter, the pressure sensitive adhesive sheet for batteries obtainedin each of Examples and Comparative Examples was attached to thepositive electrode so as to cover the entire surface of the exposed partand the entire surface of the overlapping part. At that time, thepressure sensitive adhesive sheet for batteries was made to protrude by2 mm from both end parts in the width direction of the positiveelectrode so that the exposed part would be steadily covered with thepressure sensitive adhesive sheet for batteries. In addition, thepressure sensitive adhesive sheet for batteries was made to protrude by2 mm onto the positive electrode active material layers also from bothend parts in the width direction of the exposed part.

(2) Production of Negative Electrode

A negative electrode paste was prepared by mixing 100 mass parts ofscale-like artificial graphite as a negative electrode active materialhaving an average particle diameter of about 20 μm, 1 mass part ofstyrene butadiene rubber (SER) (binder), 1 mass part ofcarboxymethylcellulose (thickener), and water. Both surfaces of copperfoil to be a negative electrode collector having a thickness of 8 μmwere coated with the obtained negative electrode paste, which was driedand then rolled to produce a strip-like negative electrode having awidth of 59 mm. Both surfaces of the end part of the negative electrodeon the winding end side were provided with exposed parts exposed fromone end part to the other end part of the negative electrode collectorin its width direction.

Then, a strip-like nickel negative electrode lead having a width of 3 mmand a length of 40 mm was overlapped and aligned with an exposed part ofthe negative electrode in the same manner as in the positive electrode,and the overlapping part was welded to the exposed part.

(3) Production of Set of Electrodes

The positive electrode and negative electrode obtained above werelaminated via separators and wound to form a set of electrodes. At thatrime, the lead-out part of the positive electrode lead was protrudedfrom one end surface of the set of electrodes while the lead-out part ofthe negative electrode lead was protruded from the other end surface.

(4) Preparation of Nonaqueous Electrolyte

A nonaqueous electrolyte was prepared by dissolving LiPF₆ in a mixedsolvent of ethylene carbonate, ethyl-methyl carbonate, and dimethylcarbonate (volume ratio of 1:1:8) to a concentration of 1.4 mol/L.

(5) Production of Battery

The set of electrodes interposed between a lower insulating ring and anupper insulating ring was housed in an iron battery case (diameter 19mm, height 65 mm) having an inner surface plated with nickel. At thattime, the negative electrode lead was made to lie between the lowerinsulating ring and the bottom part of the battery case. In addition,the positive electrode lead was made to pass through a through-hole atthe center of the upper insulating ring. Then, an electrode rod was madeto pass through a hollow part at the center of the set of electrodes anda through-hole at the center of the lower insulating ring, and one endpart of the negative electrode lead was welded to the inner bottomsurface of the battery case. On the other hand, one end part of thepositive electrode lead pulled out from the through-hole of the upperinsulating ring was welded to the inner surface of a sealing plateprovided with a gasket at the peripheral part. Thereafter, a groove wasformed in the vicinity of the opening of the battery case, and thenonaqueous electrolyte was poured into the battery case to impregnatethe set of electrodes. Then, the opening of the battery case was closedwith the sealing plate, and the opening end part of the battery case wasswaged to the peripheral part of the sealing olate via the gasket tocomplete a cylindrical nonaqueous electrolyte secondary battery (energydensity of 700 Wh/L).

(6) Execution of Forced Internal Short Circuit Test

Using the nonaqueous electrolyte secondary battery obtained above, theforced internal short circuit test for the battery was performed inaccordance with JIS C8714: 2007. Nickel pieces of a standard size(height 0.2 mm, width 0.1 mm, L-shaped with a side of 1 mm, angle 90°)and a larger size (height 0.5 iron, width 0.2 mm, L-shaped with a sideof 3 mm, angle 90°) than the standard size were prepared. The nickelpieces were disposed between the pressure sensitive adhesive sheet forbatteries and the separators so as to penetrate the pressure sensitiveadhesive sheet for batteries. Then, the forced internal short circuittest was performed to measure the rise in temperature (° C.) of thebattery side surface with a thermocouple. Results are listed in Table 1.

Details of the simplified names listed in Table 1 and additionalinformation are as follows.

<Inorganic Fine Particles>

Calcium carbonate: Calcium carbonate fine particles (available fromKonoshima Chemical Co., Ltd., product name “Calcium Carbonate Light,”average particle diameter: 1.1 μm, refractive index: 1.69)

Aluminum hydroxide 1: Aluminum hydroxide fine particles (available fromNippon Light Metal Co., Ltd., product name “BF013,” average particlediameter: 1.2 μm, refractive index: 1.57)

Alumina: Alumina fine particles (available from Denka Company Limited,product name “ASFP-20,” average particle diameter: 0.26 μm, refractiveindex: 1.76)

Titania: Titania fine particles (available from Sakai Chemical IndustryCo., Ltd., product name “R-310,” average particle diameter: 0.2 μm,refractive index: 2.64)

Aluminum hydroxide 2: Aluminum hydroxide fine particles (available fromShowa Denko K.K., product name “Higilite H42,” average particlediameter: 1.0 μm, refractive index: 1.57)

TABLE 1 Pressure sensitive adhesive layer Inorganic fine particlesContent in pressure Average Additive sensitive Total particle amountadhesive Haze luminous diameter Refractive (mass layer valuetransmittance Type (μm) index parts) (vol %) (%) (%) Example 1 Calciumcarbonate 1.1 1.69 27.5 10 63.5 95.6 Example 2 Aluminum hydroxide 1 1.21.57 55 20 73.4 96.7 Example 3 Aluminum hydroxide 1 1.2 1.57 95 30 75.095.2 Comparative Example 1 Alumine  0.26 1.76 90 20 86.3 75.8Comparative Example 2 Titania 0.2 2.64 100 20 99.6 36.5 ComparativeExample 3 — — — — — 0.5 99.9 Comparative Example 4 Aluminum hydroxide 11.2 1.57 500 70 95.5 80.0 Comparative Example 5 Aluminum hydroxide 2 1.01.57 24   9.8 45.0 98.0 Pressure sensitive adhesive sheet for batteriesEvaluation of insulation properties (° C.) Total Suitability Small Hazeluminous Adhesive for foreign pieces of value transmittance strengthmaterial standard Small pieces (%) (%) (N/25 mm) inspection size oflarger size Example 1 64.4 53.3 1.2 ◯ 10 15 Example 2 73.5 53.9 1.2 ◯ 1520 Example 3 74.4 52.5 0.8 ◯ 5 10 Comparative Example 1 84.0 39.6 1.0 X10 15 Comparative Example 2 99.6 16.0 1.6 X 15 20 Comparative Example 37.6 56.4 2.8 ◯ 36 >100 Comparative Example 4 96.0 40.1 0.1 X 5 10Comparative Example 5 44.1 55.1 1.5 ◯ 22 >100

As apparent, from Table 1, the pressure sensitive adhesive sheets forbatteries of Examples have high insulation properties and it is possibleto suppress the temperature rise due to the forced internal snortcircuit test and well perform the foreign material inspection.

INDUSTRIAL APPLICABILITY

The pressure sensitive adhesive composition and the pressure sensitiveadhesive sheet for batteries according to the present invention aresuitable for use inside a lithium-ion battery and, in particular,suitable for attaching an electrode lead-out tab to an electrode.

DESCRIPTION OF REFERENCE NUMERALS

-   1 . . . Pressure sensitive adhesive sheet for batteries    -   11 . . . Base material    -   12 . . . Pressure sensitive adhesive layer        -   121 . . . inorganic fine particles    -   13 . . . Release sheet-   2 . . . Lithium-ion battery    -   21 . . . Exterior body    -   22 . . . Positive electrode terminal    -   23 . . . Negative electrode terminal    -   24 . . . Electrode body        -   241 . . . Positive electrode collector        -   241 a . . . Positive electrode active material layer        -   242 . . . Negative electrode collector        -   242 a . . . Negative electrode active material layer        -   243 . . . Separator        -   244 . . . Electrode lead-out tab

1. A pressure sensitive adhesive sheet for batteries, comprising: a basematerial; and a pressure sensitive adhesive layer provided on onesurface side of the base material and containing inorganic fineparticles, wherein a haze value of the pressure sensitive adhesive layeris 50% or more and 85% or less.
 2. The pressure sensitive adhesive sheetfor batteries as recited in claim 1, wherein a total luminoustransmittance of the pressure sensitive adhesive layer is 80% or more.3. The pressure sensitive adhesive sheet for batteries as recited inclaim 1, wherein a content of the inorganic fine particles in thepressure sensitive adhesive layer is 1 vol % or more and 50 vol % orless with respect to the pressure sensitive adhesive layer.
 4. Thepressure sensitive adhesive sheet for batteries as recited in claim 1,wherein a thickness of the pressure sensitive adhesive layer is 1 μm ormore and 50 μm or less.
 5. A lithium-ion battery in which two or moreconductors are fixed in a state of being in contact with each otherinside the battery using the pressure sensitive adhesive sheet forbatteries as recited in claim 1.